We report a relative humidity sensor based on manganese-nanoparticle-loaded mesoporous silica SBA-15 using a facile hydrothermal route. The as-developed nanocomposite material (Mn/SBA-15) possesses a high surface area and a high pore volume. The obtained samples were characterized by using low-angle X-ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), N-2 adsorption-desorption, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy techniques. The Mn/SBA-15 exhibited, improved humidity response and recovery time as compared to pure SBA-15 in the 11%-92% RH range. Optimal results were obtained for the 5wt% Mn-loaded SBA-15 sample, which displayed excellent linearity, low hysteresis, and high humidity response. A change in similar to 5 orders of magnitude in resistance was observed over 11%-92% RH range. The investigation of humidity sensing properties of Mn/SBA-15 nanocomposite shows that this material has good prospects as humidity sensor.